Exploring large wood retention and deposition in contrasting river morphologies linking numerical modelling and field observations

Large wood tends to be deposited in specific geomorphic units within rivers. Nevertheless, predicting the spatial distribution of wood deposits once wood enters a river is still difficult because of the inherent complexity of its dynamics. In addition, the lack of long‐term observations or monitored sites has usually resulted in a rather incomplete understanding of the main factors controlling wood deposition under natural conditions. In this study, the deposition of large wood was investigated in the Czarny Dunajec River, Polish Carpathians, by linking numerical modelling and field observations so as to identify the main factors influencing wood retention in rivers. Results show that wood retention capacity is higher in unmanaged multi‐thread channels than in channelized, single‐thread reaches. We also identify preferential sites for wood deposition based on the probability of deposition under different flood scenarios, and observe different deposition patterns depending on the geomorphic configuration of the study reach. In addition, results indicate that wood is not always deposited in the geomorphic units with the highest roughness, except for low‐magnitude floods. We conclude that wood deposition is controlled by flood magnitude and the elevation of flooded surfaces in relation to the low‐flow water surface. In that sense, the elevation at which wood is deposited in rivers will differ between floods of different magnitude. Therefore, together with the morphology, flood magnitude represents the most significant control on wood deposition in mountain rivers wider than the height of riparian trees. Copyright © 2015 John Wiley & Sons, Ltd.     

Alongshore variability of cross‐shore bar behavior on a nontidal beach

We report on a 6‐year nearshore bathymetric dataset from the Danube Delta (Romanian Black Sea coast) that comprises 16 km of erosive, stable and accumulative low‐lying micro‐tidal beaches northward of Sf. Gheorghe arm mouth. Two to three two‐dimensional longshore sandbars exhibit a net multi‐annual cyclic (2.8–5.5 years) offshore migration (20–50 m yr^?1) in a similar way to other coasts worldwide. Bar morphology and behavior on the sediment‐rich accretionary (dissipative) sector differ substantially from that on the erosive (intermediate) sector. Shoreface slope is the most important factor controlling sandbar number and behavior. It determines different wave‐breaking patterns in the surf zone, translated into different offshore sediment transport and bar zone widths along the study site. Additionally, sediment availability, as a result of the distance from the arm mouth and of the long‐term evolution of the coast, controls the sandbar volume variability. These are all ultimately reflected in the variations of sandbar migration rates and cycle periods. A non‐dimensional morpho‐sedimentary parameter is finally presented, which expresses the bar system change potential as offshore sediment transport potential across the bar zone. Copyright © 2016 John Wiley & Sons, Ltd.     

强震动作用下土体非线性动力特征研究发展与展望

浅地表覆盖土层动力特性对地震动影响显著,软厚土层会明显改变地震动强度及频谱特性。由于观测数据匮乏,强震动作用下土体非线性动力特征研究长期以来均以室内试验为主,但在实验室中难以可靠地模拟实际地震历程中土体承受的加载路径、边界条件、排水条件等复杂因素。近二十年来竖向台阵(至少包含一个地表测点和一个井下基岩测点)记录数据大量增加,为土体非线性动力学研究提供了新的基础数据与发展机遇,使基于现场观测的土体非线性动力特征实证研究成为可能。     

辽宁沉积盖层建造组合与构造古地理时空演化关系讨论

以板块构造学说为指导,以大陆动力学理论研究大陆块体离散、会聚、碰撞、造山的大陆动力学过程为主线,划分了陆块构造演化阶段.辽宁省由胶辽陆块、晋冀辽陆块2个Ⅰ级构造古地理单元组成;Ⅱ级构造古地理单元3个,即辽东陆内、燕辽裂谷、燕辽陆内;Ⅲ级构造古地理单元11个;Ⅳ级构造古地理单元14个.利用沉积岩建造组合与构造古地理单元时空结构演化关系,为研究辽宁省大地构造环境演化提供较系统的基础地质资料.     

中国城市用地与人口规模分布时空动态比较——以环渤海地区为例

复合1992-2012年DMSP/OLS稳定夜间灯光等多源遥感数据和统计数据,运用多种城市规模分布理论方法,对城市用地与人口规模分布时空演变特征进行系统比较。结果表明：环渤海地区城市用地规模增长速度明显快于城市人口规模增长速度,城市人口规模分布比城市用地规模分布更为均衡;城市用地规模呈首位型分布但首位优势在减弱,城市人口规模呈位次型分布但首位优势在增强;位序迅速上升的城市主要位于山东省和河北省,位序显著下降的城市主要位于辽宁省。环渤海地区城市规模空间分布呈显著的区域差异和空间极化特征,且城市用地规模分布空间特征比城市人口规模分布更为突出。研究结论可为优化区域城市空间开发格局、促进人地系统可持续发展提供参考。     

Coastal erosion in response to wave dynamics operative in Sagar Island, Sundarban delta, India

Coastal erosion at Sagar Island of Sunderban delta, India, has been critically studied. The area is in the subtropical humid region. There are mainly three seasons viz: winter, summer and the monsoon. Different wave dynamic parameters were measured from theodolite observations with leveling staff and measuring gauges during lunar days at two sections of the western and eastern parts of the coastal zone during post-and pre-monsoons. A comparative study was made on the erosion/depositional pattern between the two sections in relation to different hydrodynamic parameters prevailing in these two sections. Plane table mapping was carried out to demarcate the different geomorphic units. The marine coastal landforms show dune ridges with intervening flats bordered by gently sloping beach on one side and a flat beach on the other side. The western part of the beach is mainly sandy; whereas the eastern part is silty and clayey with mud bank remnants. Actual field measurements indicate that the coastal dune belt has retreated to the order by about 20 m since 1985. The eastern part of the beach has lowered by about 2 m since 1985 and the western part was raised almost to the same tune. It is observed that accretion in the western and central parts of the beach took place; whereas severe erosion in the eastern part made the beach very narrow with remnants of mud banks and tree roots. Frequent embankment failures, submergence and flooding, beach erosion and siltation at jetties and navigational channels, cyclones and storm surges made this area increasingly vulnerable.     

Coastal landslides and swelling clays at Røsnæs,Denmark

Prior, D. B., 1973: Coastal landslides and swelling clays at Røsnæs, Denmark. Geografisk Tidsskrift, 72: 45–48. København, September 30, 1973.

The landslide morphology of the Røsnæs area has been examined and materials involved in active landsliding analysed.     

A GIS-Based Tool for Representing Larval Dispersal for Marine Reserve Selection

Increasing efforts to implement marine protected areas (MPAs) as a means of managing marine ecosystems have created a need for evaluating potential spatial management plans. Almost all marine populations are metapopulations, connected reproductively by the dispersal of pelagic larvae. Models of marine population dynamics must account for larval connectivity, but despite recent advances connectivity patterns are still poorly understood. To allow more informed decision making when complete information on dispersal is lacking, we have developed a method based on geographic information systems (GIS) for representing larval dispersal distributions based on bathymetry and typical flows in the coastal ocean. These distributions reflect (1) generally greater flow in directions along, rather than across, lines of constant bathymetry and (2) lesser flow in shallow near-shore waters. We demonstrate how to parameterize this two-dimensional method for depicting larval dispersal based on comparisons to local oceanographic data. We then compare the predictions of the two-dimensional method to those of a simpler one-dimensional alternative in a population model used to evaluate proposed MPAs along the coast of central California. The method produces reasonable larval dispersal patterns and appears to include the effects of bathymetry on population dynamics better than commonly used one-dimensional methods and without requiring the significantly greater investment of developing particle-tracking circulation models. An important advantage of a two-dimensional approach is more realistic portrayal of the dependence of population persistence on the cross-shelf dimension of available habitat.     

Biogeography and Genetic Diversity of Pearl Millet (Pennisetum glaucum) from Sahelian Africa

Sahelian Africa makes up the native range of pearl millet and the impact of domestication on the genetic diversity of wild, intermediate, and cultivated subspecies is still poorly understood. Wild populations are known to spontaneously germinate throughout this range and hybridize with cultivated material. To investigate genetic structure, populations of pearl millet from several African countries were analyzed at the morphological and molecular levels for diversity. Results demonstrate how little differentiation there is between subspecies and populations. It appears that pearl millet throughout the Sahel remains a metapopulation with large hybrid zones. These results have important implications for conservation of pearl millet.